ENDOGENOUS ABSCISIC-ACID LEVELS ARE LINKED TO DECREASED GROWTH OF BUSH BEAN-PLANTS TREATED WITH NACL

This paper studies the relative importance of endogenous ABA and ion t oxicity in the leaf growth inhibition caused by NaCI in salt-adapted a nd unadapted bush beans. Adaptation to salt-stress was achieved by ger mination of seeds in 75 mM NaCI, while unadapted plants were germinate d in tap water. The adaptation process caused a transitory increase in leaf ABA, Na+ and Cl- concentrations, while leaf expansion was inhibi ted. However, when grown for 8 or 13 days in 75 mM NaCl-containing nut rient solution, primary and first trifoliolate leaves of salt-adapted plants had greater areas than those of unadapted plants. Concentration s of ABA, Na+ and Cl- in these leaves were lower in adapted plants, an d a strong negative correlation between leaf expansion growth and eith er leaf Na+, Cl- or ABA concentrations could be established. However, in the second trifoliolate leaves only the ABA, but not the Na+ or Cl- , concentrations were significantly correlated with leaf expansion. Ou r results suggest that salt-induced inhibition of leaf expansion growt h in bush beans is mediated by ABA rather than Na+ or Cl- toxicity. Mo reover, the increase of ABA, induced by the salt-pretreatment, seems t o play an important role in limiting the accumulation of Na+ and Cl- i n the leaves, leading to adaptation of bush beans to salt-stress.